The Commission was informed about the illegal behaviour in January 2001, when Mueller Industries approached it under the 1996 Leniency Notice, which enables a company to escape a fine if it is the first to reveal the existence of a cartel.

An investigation by the Commission then discovered that the companies had operated a cartel between June 1988 and March 2001 that allocated production volumes and market shares, set price targets and price increases for plain copper plumbing tubes. It also found that the KME and the Wieland groups had operated a similar cartel for plastic-coated copper plumbing tubes.